The invention relates to a driving motor for an electric car which rotates an input shaft of the electric car.
FIG. 2 is a longitudinal section view of a prior art driving motor for an electric car. In the figure, 1 designates an induction motor having the following configuration. The reference numeral 2 designates a stator core having slots in which a stator winding 3 is formed, 4 designates a rotor core secured to a rotating shaft 8, and 5 designates rotor conductors which are disposed in slots of the rotor core 4 and connected to each other by end rings 6 to be united into one body. The reference numeral 7 designates fans formed on the end rings 6, 9 designates an intermediate bracket, 10 designates a front bracket at an output (work) side of the motor, and 11 designates a rear bracket at non-work side of the motor. These brackets and the stator core 2 are combined with each other by through bolts 12. The front end portion of the rotating shaft 8 is supported through a ball bearing 13 by the intermediate bracket 9, and the rear end portion is supported through a ball bearing 14 by the rear bracket 11. The reference numeral 15 designates baffle plates which are disposed inside the intermediate bracket 9 and partition the space into an inlet and-outlet for cooling air.
The reference numeral 16 designates an epicycle reduction gear having the following configuration. The reference numeral 17 designates a sun gear which is a pinion positioned at the front end of the rotating shaft 8, and 18 designates a plurality of planet gears which engage with the sun gear 17 and are supported through a bearing 20 by a supporting pin 19. The reference numeral 21 designates an internal gear which is fixed to the inside of the front bracket 10 and functions so as to revolve the engaging planet gears 18, and 22 designates an output carrier to which the supporting pin 19 is fixed and which transmits the reduced rotation. The front portion of the output carrier 22 is supported through a ball bearing 23 by the front bracket 10, and the rear end is supported through a ball bearing 24 by the intermediate bracket 9.
The reference numerals 25 and 26 designate oil seals for sealing the lubricating oil in the epicycle reduction gear 16, 27 designates a cap fitted onto a lubricating oil supply port of the intermediate bracket 9, and 28 designates a flange coupling which is connected with the shaft end of the output carrier 22 by a key 31 inserted between them and also by a combination of a bolt 30 and a washer 29. The flange coupling 28 is connected with an input shaft of the electric car. The reference numeral 32 designates a speed sensor having a rotating unit attached to the rear end portion of the rotating shaft 8, and a fixed unit supported by the rear bracket 11.
When the electric car is to be driven by the driving motor having this configuration, a low frequency and polyphase (e.g., three-phase) AC voltage is firstly supplied from a power supply mounted on the car, to the induction motor 1. This causes the rotating shaft 8 to rotate at a low speed. This rotation is reduced in speed by the epicycle reduction gear 16, and then transmitted through the output carrier 22 to the input shaft of the electric car, thereby causing the electric car to run. The speed sensor 32 detects the speed. As the frequency of the voltage supplied to the induction motor 1 is raised, the speed of the electric car is increased.
In the prior art driving motor, the rotating shaft 8 is supported through the ball bearings 13 and 14 by bearing boxes of the intermediate bracket 9 and the rear bracket 11. The axial direction support of the rotating shaft 8 is realized by the configuration in which a step portion of the front end of the shaft is received in the inner end of the inner ring of the ball bearing 13 and a step portion of the rear end is received in the inner end of the inner ring of the ball bearing 14. The outer end of the outer ring of the ball bearing 13 is received by a step portion of a bearing box of the intermediate bracket 9, and the outer end of the outer ring of the ball bearing 14 is received by a step portion of a bearing box of the rear bracket 11. In view of the variation in dimension in the axial direction which is caused by the accumulation of machining dimensional tolerances of the components, the distance between the step portion of the bearing box of the intermediate bracket 9 and the step portion of the bearing box of the rear bracket 11 is previously set to be a sufficiently larger value than the dimension between the outer end of the ball bearing 13 having the inner ring secured to the front end of the rotating shaft 8 and the outer end of the ball bearing 14 having the inner ring fixed to the rear end of the rotating shaft 8.
In such a prior art driving motor for an electric car, the induction motor 1 is so constructed that the distance between the step portion of the bearing box of the intermediate bracket 9 and the step portion of the bearing box of the rear bracket 11 is set to be sufficiently larger than the dimension between the outer ends of the outer rings of the ball bearings 13 and 14 each having the inner rings secured to the rotating shaft 8, and that each of the outer rings is loosely fitted into the inner periphery of the respective bearing box. Therefore, there exists a problem in that the rotating shaft 8 can move in a certain range in the axial direction, thereby causing a noise. Furthermore, there exists another problem in that, as the balls in the bearing boxes of the intermediate bracket 9 and the rear bracket 11 rotate, the outer rings of the ball bearings 13 and 14 slowly rotate to produce streaks or scratches due to abrasion on the outer surfaces of the outer rings and inner surfaces of the bearing boxes, thereby causing the bearings to be damaged.
The inner ring of the ball bearing 13 disposed in the load side is pressingly fitted onto the front end portion of the rotating shaft 8. In order to place the oil seal 25 of the load side at its position, therefore, the oil seal 25 must have an inner diameter which is sufficiently large so that the oil seal can pass over the outer diameter of the outer ring of the ball bearing 13, requiring the outer periphery of the rotating shaft 8 which corresponds to and contacts with the oil seal, to have a larger diameter. This causes the rotating shaft to rotate at a higher peripheral speed, resulting in a shortened life and lowered sealing properties of the oil seal 25. Moreover, there arises a problem in that the rotating shaft 8 must be produced from a bar material having a larger diameter.